For some time electric motor vehicles have been used both in limited private sectors, for example in the form of fork lift trucks or the like, and in road traffic, for example in the form of passenger vehicles and motor cycles. A considerable problem associated with rechargeable battery-operated vehicles is the restricted range they have, for which reason the use of such vehicles is usually limited to urban traffic and short-distance interurban traffic. A complicating factor is also that electric motor vehicles are only ready to use again after a relatively long charging time of typically 1-2 hours, which is in stark contrast to the very quick filling operation for conventional vehicles, which typically takes less than 5 minutes.
In order to circumvent the problem of the limited energy content of rechargeable batteries, it is known to use additional systems for range extension (range extenders). Range extenders is the term used for additional equipment in an electric motor vehicle which extend the range of the vehicle. Internal combustion engines which drive a generator which in turn supplies power to the rechargeable battery and the electric motor are often used for this purpose. A further example of a range extender is a fuel cell, which can be “refueled” relatively quickly with hydrogen and oxygen. For example, DE 101 33 580 discloses such a vehicle.
One problem with the known apparatuses consists in that they are not emissions-free in the case of the internal combustion engine. An argument against the use of in particular hydrogen-oxygen fuel cells is the high risk potential of the gases required for operating the cell.
It is also known to use redox flow cells for operating an automobile. The redox flow cell is a rechargeable battery which stores electrical energy in chemical compounds, wherein the reaction partners are present in dissolved form in a solvent. The two energy-storing electrolytes circulate in this case in two separate cycles, between which ion exchange takes place in the cell by means of a membrane. The cell voltage of the redox flow cell is between 1.0 and 2.2 V in practical systems. The possibility of exchanging a consumed electrolyte for an unconsumed electrolyte at a filling station is advantageous. The consumed electrolyte can be regenerated there again with current from the public power supply system. The charging or filling operation in this case lasts approximately as long as the filling operation for conventional automobiles.
Problems associated with the use of the redox flow cell in an automobile consist in the low energy content thereof and the poor dynamics. The former prevents long ranges, and the latter prevents quick accelerations of the vehicle. Redox flow cells are therefore only suitable for a niche sector.